Carburetor



Aug. 14, 1945.

S. W. GILBERT CARBURETOR v Filed July so, 1943 o o 0 0 Y In \ll') r" t a 3 M 0 \NVENTOR I jTANLE) W 51555 7- L AGENT Patented Aug. 14, 1945 CARBURETOR Stanley W. Gilbert, Middletown, Conn., assignor to Chandler-Evans Corporation, South Meriden, Conn., a corporation of Delaware Application July 30, 1943, Serial No. 496,750

1 Claim.

This invention relates to flow controlling devices, and especially to such devices as are adapted for use in carburetors for internal combustion engines.

In carburetors adapted for use on aircraft engines, the fuel flow is sometimes proportioned to I the air flow by' measuring the air and fuel flows and operating the fuel regulator valve in accordance with the balance between the measured air and fuel flows.

It is an object of the present invention'to provide an improved device for measuring and comparing two fluid flows.

A further object of the present invention is to provide improved means for measuring and com paring the fuel and air flows in a carburetor for an internal combustion engine.

A further object is to provide an improved valve structure which responds to the difference between two differential pressures. A still further object is to provide such a device in which the two differential pressures are measured by flexible diaphragms connected to the valve.

Another object of the present invention is to provide improved flow measuring and controlling means of the type described in the co-pending application of Milton E. Chandler, Serial No. 493,- 071, filed July 1, 1943.

Other objects and advantages of the present invention will become apparent from a, consideration of i the appended specification, claim and drawing, in which The single figure represents, somewh'at diagrammatically, a carburetor for an internal combustion engine embodying my invention.

Referring to the drawing, there is shown a portion It of the main body of the carburetor. Air flows thru the carburetor from an inlet thru a venturi restriction l2 and a e l3, past a throttle l4 and a fuel discharge nozzle i5 to an outlet l5.

A second air passage connects the inlet II and the throat of the venturi l2. The second air passage may be traced from the inlet I-thru a number of impact tubes ll, whose open ends are exposed to the incoming air, a vent ring l8 which interconncts the impact tubes II, a conduit 25, an expansible chamber 2| in a pressure meter 22, a restriction 22, an expansible chamber 24 in the pressure meter 22, a conduit 25, a chamber 26 and a conduit "to the throat of venturi l2.

A flexible bellows 24 is mounted in the chamber 25, and operates a valve 34 which controls the flow of air from the conduit 25 into the chamber 24. The bellows 28 is filled with nitmen or other temperature responsive fluid, so that the valve 30 is positioned as a function of the'pressure and temperature, and hence of the density of the air in chamber 26 The valve 30 controls the flow of air thru the second passage previously described in such a manner that the pressure differential established between chambers 2| and 24 is an accurate measure of the quantity of air passing thru the main air passage i3. The valve 30 compensates for variations in the pressure differentials between the inlet II and the throat of venturi l2 due to changes in density in the air, and also compensates for errors due to the inherent limitations of the venturi as a fluid meter.

The fuel passing thru the carburetor comes from a fuel pump or other suitable source of fuel under pressure (not shown) and passes thru a conduit 3|, a fuel regulator unit 32, a conduit 33, a metering restriction 34, a conduit 35, a pressure. regulator 35, and a conduit 31 to the discharge nozzle i5.

The pressure meter 22 includes, in addition to the chambers 2| and 24, a pair of expansible chambers 40 and 4|, separated by a flexible diaphragm 42. A flexible diaphragm 44 separates the chambers 2| and 24. The diaphragms 42'and 44 are suitably attached to a, valve member 45.'

A stationary transverse wall 45 extends across the chamber 40, and is provided near its center with a guide and seat member 41. The member 41 cooperates with the valve member 45 to guide its movements. The valve 45 has a passage 48 extending thru its center. and a lateral passage 49 which extends radially outward thru the valve member 45 from passage 48. The seat member 41 cooperates with the passage 49 so as to open or close th'e latter to a greater or less extent depending upon the.position of valve member 45. A sealing diaphragm 43 connects the valve member 45 and the wall 46 ata point spaced from the guide member 41, thereby forming a small chamber 80, The chamber is connected thru a passage 8| with the passage 48 extending thru the valve member45. v

The diaphragm 44 is attached to the valve member 45 by a flexible wire or cable 5|.

The fuel regulator 32 includes .a housing 52 whose interior is separated by a flexible diaphragm 52 into expansible chambers 54 and 55. The chambers 54 and 55 are interconnected thru a restriction 55 and the chamber 55 is connected to the outlet conduit 33. The diaphragm 53 carries at its center a valve 51, which is balanced against 'sition of valve SI.

inlet pressure. Acompressionspring I8 biases whose interior is separated by diaphragm 82 into expansible chambers 43 and 44. Th'e diaphragm 02 carries at its center a valve I, which is ba1-. anced against outlet pressure, and which is biased towardclosed position by a compression spring 68.

Operation As previously described, the pressure diflerential between chambers 2| and 24 is a measure of the quantity of air flowing-thru the passage ii.

The pressure differential between chambers ML and 4|, on the other hand, is a measure oi. the

- quantity of fuel flowing thru the metering restriction l4. The pressure in chamber 4| is the same as that on the downstream side of restriction 34, since chamber 4| is connected thru a conduit 81 to the chamber 63 of the pressure regulator 38. The pressure in chamber 40 is'the same as that in chamber 54 of the fuel regulator 32 since these two chambers areinterconnected by a conduit '8.

A portion of the fuel entering the chamber 54 passes thru restriction ll, chamber I4, conduit 4|, chamber 4|, passages 40 and 4|, chamber 4|, and conduit 41 to the chamber 83 in the pressure regulator 34. The quantity of fuel flowing along this path is controlled by the position of valve 4! with respect to the seat 41.

It may be seen that upon an increase in the quantity of air flowing thru the passage ",the Pressure diiferential between chambers ,2! and I4 is increased, thereby causing a movement of valve 44 to the left, to increasingly restrict the a passage between members 44 and 4|.

creases the pressure in chamber 40, which increase is transmitted thru conduit '8 to chamber I4 in the fuel regulator 32, thereby causing a movement of valve 41 in an opening direction. This increases the quantity of fuel going thru the valve 51 and the metering restriction 34 to the discharge nomle II, to match the increased quantity of air entering the carburetor.

The pressure regulator 36 operates to maintain a, substantially constant pressure on the downstream side of the metering restriction 34. The chamber '4 is vented thru a conduit Ill to the vent ring II to permit easy movement of diaphragm 82. The pressure in chamber 83 and, the force of spring G6 are large compared to the pressure in chamber 64, and the latter pressure therefore has little or no effect on the po- However, variations inthe pressure in chamberjlwhich may occur due to changes in atmospheric pressure in chamber 44 the diaphragm 44 acts to move the valve 45 to the left since the pressure in chamber 2| is always higher than the pressure in chamber 24. other hand, the diaphragm 42 always acts to move the valve 45 to the right, since the pressure in chamber 40 is always higher than the pressure in chamber 4|. The valve member 45 and the cable 5| are therefore always maintained under tension. This tensioning effect prevents a binding action between the valve 45 and the guide 41, such as might occur if the valve member 46 were acted on by two opposing compressive forces.

If two opposing forces acting at opposite ends of an elongated member so as'to stress the member in compression are slightly eccentric, they I constitute a couple tending to rotate the meme Thisin-.

or from other causes, are balanced by the action of the pressure meter 22. Changes in pressure in chamber 83 are transmitted to chamber 41 of pressure meter 22, thereby moving valve '45 and causing a parallel change in pressure in cham-- ber 44 of pressure meter 22 and in chamber 44 of fuel regulator 32, so that a balancing change is produced in the pressure upstream from the metering restriction 34. The pressure diiferential ber in a direction to increase the moment arm of the couple. If, on the other hand, the two opposing eccentric forces act so as to place the member in tension, the resulting couple tends to rotate the member in a direction to decrease the moment arm of the couple. Where the member in question is guided, as in the case of the valve 45 in the present construction, its rotation by such a couple is limited by a reactive couple 5 acting thru the walls of the guide. Altho the rotation of the valve 45 by such eccentric forces inthe present construction could be .only a very small amount, nevertheless there would be some rotation. In a given device, the moment arm of the reactive couple i fixed by the dimensions of the guide, while the moment arm of the couple applied to the ends of the valve is greater if the member is in compression than if his in I tension. It follows that the forces of the reactive. couple must be greater if the member is in compression. If these forces, which hold the valve against the. guide, are greater, then there is a greater tendency for the valve .tobind or stick. Therefore, an arrangement such as that illustrated provides a distinct advantage over devices of the type where the member connecting the diaphragms isin compression.

Furthermoreby the use of the flexible cable 5|, any force which acts laterally (vertically, in the position shown in the drawing) on the diaphragm 44 or its supporting disks cannot be transmitted to the valve 45 to hold thelatter against the guide. 7

It should also be noted that since diaphragm 44 is made larger than the diaphragm 42, a given air pressure diflerential balances a larger fuel pressure differential in the pressure meter 22.

By virtue of this construction, it is posible to use a higher pressure differential across the metering restriction 34, and hence a wider range of pressure diiferentials, permitting more accurate control of the fuel flow, is available.

While I have shown and described a preferred embodiment of my invention, other modifications thereof will readily occur to those skilled in the art, and I therefore intend my invention to be limited only by'the appended claim.

I- claim as my invention: 1

A carburetor for an internal combustion en--- gln'e, comprising in combination, a first conduit for conveying air for combustion purposes to said engine, a venturi in said first conduit for proacres metering restriction 34 is therefore not ducing two unequal pressures therein whose difference is a measure of the rate of air flow there-' thru," a source of fluid fuel under superatmos pheric pressure, a second conduit for conveying fuel from said source to said engine, a metering restriction insaid second conduit, means conduit at the discharge side of said restriction,

first valve means for controlling the fuel pressure on the intake side of said restriction and thereby controlling thefiow of fuel therethru, means for operating said first valve means including a third conduit for by-Dassing fuel from said source around said restriction-t0 said fuel pressure regulating means, said third conduit including a restriction, an expansible chamber having a movable wall attached to said first valve means for positioning the same, and second valve means for controlling the flow of fluid thru said third conduit and thereby the pressure in said chamber and the position of said first valve means, and operating -means for said second vaive means comprising two pairs of expansible chambers, 'two flexible diaphragms, each separating one of said pairs of chambers, one of said diaphragms having a greater area than the second, means for conveying air at said two unequal pressures to the two chambers separated by means.

said one diaphragm, means subjecting the two chambers separated bysaid second diaphragm to the fuel pressures upstream and downstream from said second valve means, means for connecting the two diaphragms and extending between the high pressure sides thereof including a s'rAmEY w. GILBERT. 

